A conventional FM-CW radar adopting a Frequency Modulated-Continuous Waves (FM-CW) scheme, a circuit configuration of which is relatively simple, measures a frequency of a beat signal of a frequency-modulated transmission signal and a reception signal reflected from a target object, and calculates a relative distance and relative speed with respect to the target object. A Voltage Controlled Oscillator (VCO) is provided in the conventional FM-CW radar adopting the FM-CW scheme.
The VCO outputs an oscillation frequency signal frequency-modulated according to a modulation control voltage. The oscillation frequency signal is requested to have high modulation linearity. However, because the VCO is a semiconductor device that controls a frequency with a voltage, the VCO shows a nonlinear frequency characteristic with respect to the voltage. The frequency characteristic of the VCO deviates according to individual variability or temperature characteristics. Therefore, in a shipment inspection process, work for measuring the oscillation frequency signal of the VCO and adjusting the oscillation frequency signal concerning modulation linearity is essential. The adjusting work is a hindrance to a reduction of an inspection time for mass production.
To obtain the modulation linearity of the VCO, the conventional FM-CW radar represented by Patent Literature 1 corrects the oscillation frequency signal of the VCO according to a Look Up Table (LUT) for modulation control voltage, or is provided with a mechanism for measuring the oscillation frequency signal of the VCO on a frequency modulation circuit to perform feedback control, to thereby cope with characteristic change of the VCO due to aged deterioration after shipment.